What does the cryptic crossword clue "Where to fill up spittoon later possibly? (6,7)" mean?

The wordplay uses an anagram. anagram of SPITTOON + LATER = PETROLSTATION The answer is PETROLSTATION.

Where to fill up spittoon later possibly? (6,7)

Daily Mail Cryptic #16384 | 19 Across | 2020-08-19 flower